ribbon.vert Example File

 #version 330 core

 in vec3 vertexPosition;
 in vec3 vertexNormal;

 out EyeSpaceVertex {
     vec3 position;
     vec3 normal;
 } vs_out;

 uniform mat4 modelView;
 uniform mat3 modelViewNormal;
 uniform mat4 mvp;

 uniform float time;
 uniform float amplitude = 1.0;
 uniform float lambda = 20.0;
 uniform float period = 15.0;

 //
 // Description : Array and textureless GLSL 3D simplex noise function.
 //      Author : Ian McEwan, Ashima Arts.
 //  Maintainer : ijm
 //     Lastmod : 20110409 (stegu)
 //     License : Copyright (C) 2011 Ashima Arts. All rights reserved.
 //               Distributed under the MIT License. See LICENSE file.
 //

 vec4 permute( vec4 x )
 {
     return mod(((x*34.0)+1.0)*x, 289.0);
 }

 vec4 taylorInvSqrt( vec4 r )
 {
     return 1.79284291400159 - 0.85373472095314 * r;
 }

 float snoise(vec3 v)
 {
     const vec2  C = vec2(1.0/6.0, 1.0/3.0) ;
     const vec4  D = vec4(0.0, 0.5, 1.0, 2.0);

     // First corner
     vec3 i  = floor(v + dot(v, C.yyy) );
     vec3 x0 =   v - i + dot(i, C.xxx) ;

     // Other corners
     vec3 g = step(x0.yzx, x0.xyz);
     vec3 l = 1.0 - g;
     vec3 i1 = min( g.xyz, l.zxy );
     vec3 i2 = max( g.xyz, l.zxy );

     //  x0 = x0 - 0. + 0.0 * C
     vec3 x1 = x0 - i1 + 1.0 * C.xxx;
     vec3 x2 = x0 - i2 + 2.0 * C.xxx;
     vec3 x3 = x0 - 1. + 3.0 * C.xxx;

     // Permutations
     i = mod(i, 289.0 );
     vec4 p = permute( permute( permute(
              i.z + vec4(0.0, i1.z, i2.z, 1.0 ))
            + i.y + vec4(0.0, i1.y, i2.y, 1.0 ))
            + i.x + vec4(0.0, i1.x, i2.x, 1.0 ));

     // Gradients
     // ( N*N points uniformly over a square, mapped onto an octahedron.)
     float n_ = 1.0/7.0; // N=7
     vec3  ns = n_ * D.wyz - D.xzx;

     vec4 j = p - 49.0 * floor(p * ns.z *ns.z);  //  mod(p,N*N)

     vec4 x_ = floor(j * ns.z);
     vec4 y_ = floor(j - 7.0 * x_ );    // mod(j,N)

     vec4 x = x_ *ns.x + ns.yyyy;
     vec4 y = y_ *ns.x + ns.yyyy;
     vec4 h = 1.0 - abs(x) - abs(y);

     vec4 b0 = vec4( x.xy, y.xy );
     vec4 b1 = vec4( x.zw, y.zw );

     //vec4 s0 = vec4(lessThan(b0,0.0))*2.0 - 1.0;
     //vec4 s1 = vec4(lessThan(b1,0.0))*2.0 - 1.0;
     vec4 s0 = floor(b0)*2.0 + 1.0;
     vec4 s1 = floor(b1)*2.0 + 1.0;
     vec4 sh = -step(h, vec4(0.0));

     vec4 a0 = b0.xzyw + s0.xzyw*sh.xxyy ;
     vec4 a1 = b1.xzyw + s1.xzyw*sh.zzww ;

     vec3 p0 = vec3(a0.xy,h.x);
     vec3 p1 = vec3(a0.zw,h.y);
     vec3 p2 = vec3(a1.xy,h.z);
     vec3 p3 = vec3(a1.zw,h.w);

     //Normalise gradients
     vec4 norm = taylorInvSqrt(vec4(dot(p0,p0), dot(p1,p1), dot(p2, p2), dot(p3,p3)));
     p0 *= norm.x;
     p1 *= norm.y;
     p2 *= norm.z;
     p3 *= norm.w;

     // Mix final noise value
     vec4 m = max(0.6 - vec4(dot(x0,x0), dot(x1,x1), dot(x2,x2), dot(x3,x3)), 0.0);
     m = m * m;
     return 42.0 * dot( m*m, vec4( dot(p0,x0), dot(p1,x1),
                                   dot(p2,x2), dot(p3,x3) ) );
 }

 float height( const in vec3 pos )
 {
     // Perturb the y position by a wave function in (x, t)
     const float twoPi = 2.0 * 3.14159265358979323846;
     float k = twoPi / lambda;
     float omega = twoPi / period;

     float y = amplitude * sin( k * pos.x - omega * time );

     // Further perturb by a noise function
     y += snoise( 0.27 * vec3( 0.4 * pos.x, 3.0, 2.0 * pos.z - 0.5 * time ) );

     return y;
 }

 void main()
 {
     // Calculate y value based upon input coordinates and time
     vec3 pos = vertexPosition;
     pos.y = height( pos );

     // Estimate normal vector by calculating the y value at small offsets
     // and then taking the cross product of the differences
     float offset = 0.5;
     vec3 posOffsetX = vertexPosition + vec3( offset, 0.0, 0.0 );
     posOffsetX.y = height( posOffsetX );
     vec3 posOffsetZ = vertexPosition + vec3( 0.0, 0.0, offset );
     posOffsetZ.y = height( posOffsetZ );

     vec3 dydx = posOffsetX - pos;
     vec3 dydz = posOffsetZ - pos;
     vec3 normal = cross( dydz, dydx );

     // Transform the position and normal to eye space for lighting
     vs_out.normal = normalize( modelViewNormal * normal );
     vs_out.position = vec3( modelView * vec4( pos, 1.0 ) );

     gl_Position = mvp * vec4( pos, 1.0 );
 }